Recording and erasing of data in phase-change RAM have hitherto been performed based on a change in physical characteristics caused by primary phase-transformation between a crystalline state and an amorphous state of a chalcogen compound including Te which serves as a recording material, and phase-change RAM has been designed based on this basic principle (for example, see Patent Literature 1 below).
A Recording material used for recording and erasing data in a phase-change RAM is generally formed between electrodes by using a vacuum film formation method such as sputtering. Usually, a single-layered alloy thin film made by using a target made of a compound is used as such recording material.
Therefore, a recording thin film of 20-50 nm in thickness consists of a polycrystal but not a single crystal.
A difference in interfacial electric resistance between individual microcrystals influences uniformity in electric resistance values throughout a phase-change RAM as a whole, and causes variations in resistance values in a crystalline state (see Non Patent Literature 1 below).
Furthermore, it is considered that about 10% change in volume generated in phase-transition between a crystalline state and an amorphous state causes individual microcrystals to have different stresses, and flow of material and deformation of an entire film restrict the number of times of readout of record (see Non Patent Literature 2 below).    Patent Literature 1: Japanese Patent Application Publication, Tokukai, No. 2002-203392 A    Non Patent Literature 1: supervisor: Masahiro Okuda, Zisedai Hikari Kiroku Gizyutsu to Zairyo (Technology and Materials for Future Optical Memories), CMC Publishing Company, issued on Jan. 31, 2004, p 114    Non Patent Literature 2: supervisor: Yoshito Kadota, Hikari Disc Storage no Kiso to Oyo, edited by The Institute of Electronics, Information and Communication Engineer (IEICE), third impression of the first edition issued on Jun. 1, 2001, p 209    Non Patent Literature 3: Y. Yamanda & T. Matsunaga, Journal of Applied Physics, 88, (2000) p 7020-7028Non Patent Literature 4: A. Kolobov et al. Nature Materials 3 (2004) p 703